Heat-treating of workpieces

ABSTRACT

THE INVENTION RELATES TO THE HEAT-TREATING OF WORKPIECES. A FURNACE CHAMBER HASD AN INLET AND AN OUTLET AND INCLUDES A LOWER ZONE AND AN UPPER HEAT-TREATING ZONE. ELONGATED TUBULAR GUIDE MEANS EXTENDS FROM THE INLET TO THE OUTLET IN THE LOWER ZONE AND ITS UPPER WALL PORTION WHICH FACES THE UPER ZONE IS PROVIDED WITH A LONGITUDINALLY EXTENDING SLOT. CARRIERS ARE LOCATED AND GUIDED FOR MOVEMENT WITHIN THE TUBULAR GUIDE MEANS IN AN UPRIGHT POSITION AND PROVIDED WITH WORKPIECE-SUPPORTING PORTIONS WHICH EXTEND THROUGH THE SLOT INTO THE HEAT-TREATING ZONE TO SUPPORT A WORKPIECE. RETURN GUIDE MEANS IS PROVIDED FOR GUIDING THE CARRIERS FOR RETURN MOVEMENT FROM THE OUTLET TO THE INLET OF THE CHAMBER.

March 2, 1971 R, KNAAK ET AL 3,567,200

HEAT-TREATING OF WORKPIECES 3 Sheets-Sheet 1 mea umh e; 19;9

TREATmc WP CHAMBER OUTLET' I/mLeT Erm can/s rml @gamma/a1 JJM/lean J m Waren/m March 2, 1971 R. KNAAK ET AL 3,567,200

HEAT-TREATING OF WORKPIECES Filed-March s, 1969 5 sheets-sheet z Qua/611 kum HM: Clie/:ram Pou 6th/Teo HePP Cim/sm eocemw Wailea/r 5cm/farfelu: )vw/vf 7Bn/02ML United States Patent O 3,567,200 HEAT-TREATING OF WORKPIECES Rdiger lnaak, 17 Heinestrasse, 4040 Neuss, Germany; Hans Christoph lohl, 29 Mittelstrasse, 4041 Norf, Germany; `Giinter Hepp, 159 Dieckerstrasse, 4200 Oberhausen, Germany; Christian Brockmann, 2 Franziskanerstrasse, 4300 Essen, Germany; Wilhelm Schwietering, 84 Karl Meyer Strasse, 4650 Gelsenkirchen, Germany; and Hans ,lakuhzim 42 Burgstrasse, 4680 Wanne-Eickel, Germany Filed Mar. 6, 1969, Ser. No. 804,896 lint. Cl. F27b 9/24 US. Cl. 263--8 30 Claims ABSTRACT OF THE DlSCLOSURE The invention relates to the heat-treating of workpieces. A furnace chamber has an inlet and an outlet and includes a lower zone and an upper heat-treating Zone. Elongated tubular guide means extends from the inlet to the outlet in the lower zone and its upper wall portion which faces the upper zone is provided with a longitudinally extending slot. Carriers are located and guided for movement within the tubular guide means in an upright position and provided with workpiece-supporting portions which extend through the slot into the heat-treating zone to support a workpiece. Return guide means is provided for guiding the carriers for return movement from the outlet to the inlet of the chamber.

BACKGROUND OF THE INVENTION The present invention relates generally to the heattreating of workpieces, and more particularly to the continuous heat-treating of workpieces.

Still more specifically the invention relates to a continuous heat-treating furnace for heat-treating of workpieces, and to a method of operating such a furnace.

The art knows a variety of furnaces for the heat-treating of workpieces. Among these there are the so-called pusher furnaces, the walking-beam furnaces, the tunnel furnaces and the roller-hearth furnaces. All of these different types of furnaces are of course operational for their particular purpose, but they all suffer from certain disadvantages which make them less than universally acceptable. Broadly speaking it may be said that their length from inlet to outlet frequently cannot be adequately dimensioned to obtain the desired heat-treating effect, that certain heat-resistant insulating materials cannot be used because they are subjected to excessively rough treatment in operation of the particular furnace, that the workpieces are not heated uniformly, that the components of the furnace require extremely sturdy construction which is so expensive as to be economically prohibitive in many cases. Again, in other types of furnaces the energy requirements are very high, the space requirements for guidance of the workpiece-supporting elements and return of these from the outlet to the inlet of the furnace are excessively large, or heat-treatment of workpieces is possible only within a certain temperature range. There are other disadvantages which are well enough known to those skilled in the art not to require detailed discussion.

It is, accordingly, desirable to provide a heat-treating furnace which is not possessed of the aforementioned disadvantages.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a continuous heat-treating furnace which overcomes the aforementioned disadvantages.

A more particular object of the present invention is to provide such a heat-treating furnace which is capable of being utilized with all temperature ranges required in the heat-treating of workpieces and which is capable of heating the workpiece from all sides and with maximum uniformity.

It is also an object of the present invention to provide a method of operating such a furnace.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of our invention resides in a continuous heat-treating furnace including wall means which defines a chamber provided with an inlet and an outlet and having a lower zone and an upper heat-treating zone. vElongated tubular guide means is provided which extends between the inlet and the outlet in the lower zone of the chamber and which has an upper wall portion facing the upper zone and provided with a longitudinally extending slot. Carrier means is located and guided for movement within the tubular guide means in an upright position from the inlet to the outlet and comprises a workpiece supporting portion which extends through the slot into the heat-treating zone for supporting a workpiece to be heat-treated therein. Finally, return guide means is constructed and arranged for guiding the carrier means for return movement from the outlet to the inlet of the chamber.

,It is well known that a major, if not the major, criterion for a heattreating furnace is the uniformity of heating which is imparted to the workpiece. In this conjunction it is becoming ever more important to obtain the smallest possible temperature differential between the upper side and the underside of the workpiece being heat-treated, and between the portions at which the workpiece is subjected at its underside to the effect of heating and/or rests on the workpiece support. The reason for this is that the uniformity of heat-treatment decisively influences whether the predetermined characteristics of the material can be obtained, as desired, and also whether the dimensional tolerances desired during a following forming stage can be obtained.

However, uniform heating of the underside of the workpiece is possible only if the access of heat to the workpiece is blocked as little as possible by the workpiece support and workpiece carriers. This requires that the workpiece supports and carriers be as small as possible and be well insulated. Moreover, the workpiece support must have a temperature which, at least in the contact region between the workpiece support and the workpiece, must be within the established tolerance of the selected workpiece temperature. It must be assured by the design and construction of the workpiece support that the equilibrium between heat absorption in the heattreating zone and heat withdrawal to the cooled Workpiece support results in the desired contact temperature. This, of course, requires the use of certain materials, such as highly heat-resistant metal alloys which have good hardness characteristics, are resistant to charring, fracturing and damage resulting from temperature fluctuations. The problems, however, are particularly difficult at high temperatures and under conditions where the workpiece supports carry workpieces only part of the time. It is known to those skilled in the art that workpiece supports which are so constructed that they occasion only minute temperature differences in the workpieces when they continuously support a workpiece, can be heatedparticularly in the initial heating zone of high-performance furnaces-assume temperatures which are actually in excess of the so-called furnace temperature. Under these circumstances the permissible temperature of metallic material may be exceeded and it is therefore necessary to utilize ceramic material for the upper portions of the workpiece supports, that is for the so-called riders. In certain types of furnace the treatment to which the workpiece supports are subjected during operation of the furnace may be too rough for the rather brittle ceramic material. However, in the furnace according to the present invention there are no stresses exerted on the riders which could cause damage if the same consist of ceramic material.

Furthermore, in the furnace according to the present invention the workpiece to be heat-treated continuously rests on the identical portion of the workpiece support through its entire passage through the heat-treating zone so that there are no temperature fluctuations likely to occur in the workpiece support. This is true even if workpieces are heat-treated having varying cross sections and where the spacing between the workpieces differs.

According to the present invention temperature fluctuations in the workpiece supports are to be avoided even when the same are returned from the outlet of the furnace to the inlet thereof. For this purpose at least the actual workpiece supporting portions of the workpiece supports or carriers may be guided during such return movement in special channels wherein the actual workpiece supporting portions of the carriers slowly have their temperature reducing during the return movement so that when they arrive at the chamber inlet they have the temperature of the workpieces which are to be introduced into the furnace.

From a point of view of increased lifetime the riders for the carriers, that is the workpiece supporting portions which are subjected to high or extremely high temperatures, should be of simplest possible configuration because variations in cross section and recesses and the like in these portions serve to reduce their mechanical strength and the heat conduction through them and result in internal stresses and consequent cracks in the material. According to the present invention it is therefore advantageous if the riders are simply supported on the carriers and do not require recesses or the like for connection to the carriers. This, of course, requires that the carriers on their return movement from the outlet to the inlet of the furnace are so guided that the riders cannot fall off, that is that the carriers remain substantially upright at all times. Such a construction may for instance involve carriers having an upper or workpiece supporting portion consisting of a metallic plate on which the actual rider* which consists of ceramic material-is merely supported with suitable means provided for preventing its shifting movement relative to the plate. The rider itself may consist of two or more layers of which the lower ones serve insulating purposes and may have a smaller specific weight than the upper ones which are subjected directly to the heat in the heat-treating zone. Shifting of the riders with respect to the metallic supporting plate may be prevented by suitable projections on the plate which extend laterally of the riders and thereby prevent their shifting.

The carriers are guided in hollow guide members and may be constructed as carriages provided with wheels, or as carrier members which roll on suitable rollers which are either mounted for rotation within the hollow guide members or which are arranged for free rolling movement on a bottom wall of the latter. The carriers may also be mounted on an endless metal band or analogous member which is drawn through the elongated tubular guide members sliding along the bottom wall thereof in the interior of the sarne. A further possibility is that the carriers are suitably connected in form of an endless chain which is pulled or pushed through the tubular guide members.

In any case, however, the carriers Will be provided with two main portions, namely, a main body portion located within the confines of the respective tubular guide member and a workpiece supporting portion which extends through a slot extending longitudinally of the guide member and into the heat-treating zone of the furnace. Further, it is advantageous if the workpiece supporting portion is provided with lateral extensions upwardly of CFL 4 the slot through which it extends so as to cover the slot and prevent the intrusion of contaminants through the slot into the interior of the guide members. Further, such cover portions may be provided for covering the space between successive carriers.

The elongated tubular guide members may be of different cross-sectional congurations and may be doublewalled for circulation of a cooling medium therethrough. However, it is also within the concept of the present invention to circulate the cooling medium directly through the interior of the tubular guide members in which case the main body portions of the carriers are completely or partially immersed in the cooling medium. It will be appreciated that the cooling medium may be introduced into the interior of the tubular guide members, or into the cooling jacket constituted by the double-walled construction mentioned above, at different longitudinally spaced locations, or at a single location. The cooling medium itself may be purified water to which a lubricating medium is added together with another medium having a higher flash temperature than water. Both owthrough type of cooling and evaporation cooling may be utilized. According to the invention the tubular guide members may be wholly or partially inclined to the horizontal to influence the flow of cooling medium and/or facilitate the advancement of the carriers.

The tubular guide members may in known manner be supported by cooled supports well-known to those skilled in the art. Particularly if two or more of the tubular guide members extend transversely spaced in parallelism or substantial parallelism with one another, so that long workpieces may simultaneously be supported on carriers of two or all of these guide members, the guide members may be mounted so as to be moveable with limited freedom in direction transversely to their elongation so that, when a longitudinal expansion of the workpiece takes place as a result of the heat-treatment thereof, the guide members may yield. For the same reason the carriers themselves may have a certain amount of lateral play within their respective guide members. Lateral guidance of the carriers within their respectively associated guide members may be accomplished by guidance supports provided on the respective main body portions of the carriers, and the drive effecting movement of the carriers through the guide members, for instance the teeth of a sprocket wheel used for such drive and for reversing the direction of movement of the carriers at the outlet and inlet of the chamber, may engage these guide supports if the carriers are connected in form of an endless chain.

Where, despite the aforementioned measure for preventing the intrusion of contaminants into the interior of the guide members through the slot, such contaminants do enter the bottom wall in the interior of the guide member along which the carriers move, may be provided with a longitudinally extending groove and the carriers may be provided with clean-out projections extending into this groove and pushing the solid contaminants along the groove to the outlet. Also, it is advantageous that the main body portion of each carrier is offset laterally with respect to the workpiece supporting portion extending upwardly through the slot.

The workpiece supporting portions may be constructed as, or provided with plates supported thereon, which consist of material resistant to extreme heats, particularly ceramic material, and which has high heat conductivity. This is advantageous if the workpieces to be supported are small so that they can be arranged on these plates, and it will be appreciated that each of the plates may be supported on the workpiece supporting portions of carriers located in one or more of the guide members. This provides for effective indirect heating of the underside of the workpieces. Evidently, the workpiece supports may be of different heights and the plates may then be supported only on the higher ones of the workpiece supports, or the same may of course be true of the workpieces themselves.

The tubular `guide ymeans need not be straight, but may be of circular type located in a horizontal plane, and in this case a portion of arc will constitute the chamber provided with the heat-treating zone whereas the remainder would constitute the return path for the carriers.

Return of the carriers may be accomplished within the confines of the furnace or exteriorly of the furnace, and the drive may be provided in one of the reversing rollers.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic illustration for purposes of explaining the present invention as to its principle;

FIG. 2 is a cross section through an elongated tubular guide member according to the present invention with a carrier shown therein;

FIG. 3 is a side-elevational fragmentary section of FIG. 2;

FIG. 4 illusfrates a return-guide arrangement for the carrier shown in FIG. 2;

FIG. 5 is an illustrative explanatory view, in a diagrammatic partly broken-away perspective, illustrating a further embodiment of the invention in principle; and

FIG. 6 illustrates in partial section and partial fragmentary side elevation an additional embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing in detail, and iirstly FIG. 1 thereof, it will be seen that reference numeral 1 generally identifies an elongated tubular guide means of a type and construction to be discussed further on. Reference numeral 2 indicates a plurality of carriers whose main body portions are located for movement within the tubular guide means 1 and which are provided with workpiece supporting portions extending outwardly of the tubular guide means, and supporting the workpi-eces WP. A treating chamber is designated with an appropriate legend and the wall means dening this treating chamber is diagrammatically illustrated in broken lines; it will be seen to have an inlet and an outlet. Reference numeral 3 identifies the reversing rollers for the carriers 2 which are here seen to constitute an endless chain. It should be noted that in FIG. l the carriers are so supported one on the other that each carrier is in need of only a single rolling axis. We wish to emphasize that the arrangement illustrated in FIG. 1 may be such that the return movement of the carriers 2, that is their movement from the outlet back to the inlet of the treating chamber, may occur either within or without the furnace, and in fact the rollers 3 may similarly be located either within or without the furnace.

FIGS. Q and 3 illustrate details of the construction shown in FIG. 1. The guide means 1 in FIG. 2 is assembled from a plurality of double-walled profile members 4 of prismatic cross section. The inner space 4a of each of the members 4 pro-vides a iiow bath for the circulation of cooling uid therethrough. The carriers 2 comprise, as most clearly evident from FIG. 4, a main body portion 2a and a workpiece-supporting portion including a section 2b which extends through a longitudinally extending slot provided in the upper wall 4b of the guide members 1, and a section 5 on which the actual workpiece WP is supported, as illustrated in FIG. 2. The slot 4b is provided in the upper wall of the guide members 1 which faces the heat-treating zone of the treating chamber. In the illustrated embodiment of FIG. 2 the actual guide member assembled from the members 4 is surrounded by 6 an insulation 9 of suitable material, here illustrated generally as heat insulating material. Reference numerals 7 indicate the supporting rollers for the carriers 2 and reference numerals 8 the lateral guide rollers for the same.

As shown in FIG. 3, each carrier 2 is provided with a projecting nose 6 which engages into a correspondingly congurated recess of the next adjacent carrier 2 so as to bridge the interval or spacing between the carriers to prevent the intrusion of solid contaminants from the heattreating Zone through the slot 4b into the interior of the guide members 1.

As shown in FIG. 4 the return movement of the carriers 2 may in the illustrated embodiment of FIGS. 1-4 be accomplished in special return channels CH with the carriers 2 being reversed about the downstream one of the rollers 3 so that their workpiece supporting sections 5 now are located downwardly with the rollers 7 rolling in the interior of the channels CH. This is a construction, of course, wherein the sections 5 must be rigidly connected with or be of one piece with the sections 2b.

The embodiment illustrated in FIG. 5 provides for a construction wherein it is not necessary for the carriers to be turned upside down, as in the case of FIG. 4. Here, the carriers are identified with reference numeral 9 and it will be seen that they pass through the furnace F and then enter return guide channels 10` which are located substantially in the same horizontal plane as the tubular guide members located in the interior of the furnace F. These guide members 10` communicate with the outlet end of the furnace F so that the carriers 9 can enter directly into the return channels 10 to be guided back to the inlet end of the furnace F. It is desirable that in the region of the location 11 the carriers 9 have cooled down to the ambient temperature, that is the same temperature which the articles to `be heat-treated have, that Ais the workpieces which are to be introduced at the inlet end of the furnace F. For this reason the return guide channels 10 may terminate at the location 11 because at this point the carriers 9 may 4be exposed to the ambient atmosphere. Reference numeral 12 identities rollers located at the inlet end of the furnace for supplying the workpiece, and at the outlet end the same rollers serve to remove the heat-treated workpieces. The rollers 12 may be mounted movable in vertical direction so that they can be raised or lowered to facilitate transfer of the workpeces from the rollers onto the carriers 9, or vice versa. The drive for effecting movement of the carriers 9 has not been illustrated because it may be conventional.

Coming, finally, to FIG. 6 it will be seen that the tubular guide means herein illustrated is not of double-walled construction as in FIGS. 144, but instead is intended to have its interior lled with cooling uid. Thus, the carriers which are here again illustrated as connected into an endless chain, will be immersed with their main body portions in the cooling fluid. Reference numeral 13 identies the supporting rollers on which the carriers advance, and the nose 14 provided on each carrier rests on the respectively preceding area so that only a single set of rollers 1-3 is necessary for each carrier. The pin 1S connects adjacent ones of the carriers with one another and serves at' the same time as an axis for the annular bearing 16 which provides for lateral guidance of the main body portion within the confines of the guide member. The latter `is identied with reference numeral 17 and we wish to emphasize that the annular bearing 16 may serve not only for lateral guidance but may also be engaged by the teeth of the reversing rollers at the inlet and outlet end of the furnace, the reversing rollers not being illustrated. In this embodiment, it should be understood, it is assumed that the furnace is of the general type illustrated in FIG. 5.

The turning axis of the carriers with respect to one another, that is the axis of the pin 15 and slot 17a in the guide member 17 are laterally oifset with respect to one another, as clearly visible, so that the cutouts in the workpiece supporting portions 20--which are here illustrated as of the type wherein two sections of different heatresistant materials are loosely supported on a plate portion 18a of the section 18 of the carriers-and which are necessary for permitting the lateral turning of the carriers during passage around the associated reversing rollers (not illustrated) are not located above the slot 17a so as to thereby prevent intrusion of contaminants to the latter. The supporting portion 18a is provided with upwardly extending projections 19 of highly heat-resistant material which supports both the workpiece-supporting portions 20 of ceramic material and the lateral insulating portions 21. Reference numeral 23 identifies the exterior insulation surrounding the guide member 17. The noses 22 provided on the respective carriers 18 serve to close the longitudinal gaps between adjacent ones of the carriers and each extend into a corresponding recess of the next-adjacent carrier.

The projections 19 may be integral with the portions 18a where they may be secured thereto, as for instance by welding. Advantageously the projections 19 consist of highly heat-resistant alloys.

It should still be pointed out that the return channels, such as the channels illustrated in FIG. 5, may be heated and/or cooled as necessary, that is as required to obtain a gradual reduction in the temperature of the returning carriers-or at least of their workpiece supporting portions-until in the proximity of the inlet to the furnace the carriers or their workpiece-supporting portions will again have reached the temperature of the Workpieces to be treated, that is normally the ambient temperature. If cooling is to be carried out, this can be achieved particularly in the region of the inlet of the furnace by passing air through the channels or, if the channels have already been terminated previously, over the carriers or at least their workpiece supporting portions. Heating, which will advantageously be effected in the region closer to the outlet of the furnace, can be accomplished in various different ways, for instance by using heat exhausted from the furnace.

The invention is also suitable, it should be understood, for the continuous transport of heated materials through so-called cooling beds or cooling regions.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a continuous heat-treating furnace, it is not intended to be limited to the details shown, since various modications and structural changes may be made without departing in any way from the spirit of the present invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

1. In a continuous heat-treating furnace, in combination, wall means defining a chamber provided with an inlet and an outlet and having a lower zone and an upper heat treating zone; elongated tubular guide means extending between said inlet and said outlet in said lower zone and having an upper wall portion facing said upper zone and provided with a longitudinally extending slot; carrier means located and guided for movement within said tubular guide means in an upright position from said inlet to said outlet and comprising a workpiece supporting portion extending through said slot into said heat treating zone for supporting a workpiece to be heat treated therein, said supporting portion comprising a metallic supporting plate, at least one discrete ceramic member carried `by said supporting plate located in said heat treating zone, and abutment portions for limiting movement of said discrete member with reference to said supporting plate and at least some of which are exposed to the temperature prevailing in said heat treating zone and consist of alloy resistant to such temperature; and return guide means constructed and arranged for guiding said carrier means for return movement from said outlet to said inlet.

2. In a furnace as defined in claim 1, said discrete member consisting of a plurality of layers respectively closer to and farther spaced from said supporting plate, the layers which are closer to said supporting plate having a lower specific weight than the remaining layers.

3. In a continuous heat-treating furnace, in combination, wall means defining a chamber provided with an inlet and an outlet and having a lower zone and an upper heat treating zone; elongated tubular guide means cxtending between said inlet and said outlet in said lower zone and having an upper wall portion facing said upper zone and provided with a longitudinally extending slot; carrier means located and guided for movement within said tubular guide means in an upright position from said inlet to said outlet and comprising a workpiece supporting portion extending through said slot into said heat treating zone for supporting a workpiece to be heat treated therein; and enclosed return guide means cooled at least in the region proximal to said inlet and constructed and arranged for guiding said carrier means for return movement from said outlet to said inlet.

4. In a furnace as defined in claim 3, said return guide means being constructed and arranged for guiding said carrier means for return movement outside the confines of said wall means.

5. In a furnace as defined in claim 3, said return guide means being constructed and arranged for guiding said carrier means for return movement within the confines of said wall means.

6. ln a furnace as defined in claim 3, said return guide means being constructed and arranged for guiding said carriers in substantially upright position and in a substantially horizontal path.

7. In a furnace as defined in claim 3, said supporting portion comprising a first section located in said slot when said carrier means is within said tubular guide means, and a second section located exteriorly of said slot and in said heat treating zone, at least said second section consisting of a material resistant to the temperatures prevailing in said heat treating zone.

8. In a furnace as defined in claim 7, said material of said second section being a metallic alloy.

9. In a furnace as defined in claim 7, said material of said second section being a ceramic material resistant to thermal fluctuations.

10. In a furnace as defined in claim 3, said carrier means comprising roller means supporting said carrier means for rolling movement within said tubular guide means.

11. In a furnace as defined in claim 10, said tubular guide means having a bottom wall portion opposite said upper wall portion, said roller means being supported for rolling movement on said bottom wall portion and said carriage means being supported on said roller means.

12. In a furnace as defined in claim 3, said tubular guide means including a bottom wall portion opposite said upper wall portion; and further comprising an endless metallic loop supported on said bottom wall portion for sliding advancement therealong, said carrier means being connected to said loop for movement with the same.

13. In a furnace as defined in claim 3, said carrier means comprising a plurality of individual carriers connected to one another and together constituting an endless carrier chain.

14. In a furnace as dened in claim 3, said tubular guide means having cooling means including wall portions constructed as cooling jackets for circulation of a cooling fluid therethrough.

1S. ln a furnace as defined in claim 14, further comprising cooling fluid circulating through the interior of said cooling jackets.

16. In a furnace as defined in claim 15, said cooling 9 liuid comprising a mixture of water, of a lubricating medium and of an additional medium having a ashpoint higher than Water.

17. In a furnace as defined in claim 3, said tubular guide means being inclined in longitudinal direction over at least part of its elongation.

18. 'In a furnace as defined in claim 3, said supporting portion including laterally extending ridges upwardly of said upper wall portion and covering said slot therein.

19. In a furnace as defined in claim 18, said carrier means including at least two consecutively arranged carriers with a gap therebetween, and said supporting portion of one of said carriers including a cover portion extending to the other carrier across said gap for closing the latter.

20. In a furnace as defined in claim 3, said carrier means being arranged for movement in correspondence with the longitudinal center line of said tubular guide means, and said slot being laterally offset from said tubular guide means.

21. In a furnace as defined in claim 3, and further comprising lateral guide means rigid with said carrier means and operative for effecting lateral guiding thereof within and relative to said tubular guide means.

22. In a furnace as defined in claim 3, and further comprising cooled bracing means supporting said tubular guide means with reference to said wall means.

23. In a furnace as defined in claim 2, said bracing means mounting said tubular guide means with limited freedom of lateral movement in direction transversely of their elongation.

24. In a furnace as defined in claim 3, said tubular guide means accommodating said carrier means with limited freedom of lateral play of said carrier means relative to said tubular guide means.

25. In a furnace as defined in claim 3, and further comprising advancing means associated with said carrier means and operative for effecting advancement thereof through said tubular guide means to said outlet and from the latter to said inlet.

26. In a furnace as defined in claim 25, further comprising reversing rollers arranged in the region of said inlet and said outlet, respectively, said carrier means being guided for movement about said reversing rollers;

and said drive means being arranged within and operative for driving one of said reversing rollers.

27. In a furnace as defined in claim 3, said carrier means comprising a plurality of individual carriers, and said supporting portions of different ones of said carriers projecting through said slot and into said heat-treating zone by different distances.

28. In a furnace as defined in claim 3, said tubular guide means being elongated in a substantially circular configuration.

29. In a furnace as defined in claim 28, said heating zone extending along said tubular guide means over only a portion of arc.

30. In a continuous heat-treating furnace, in combination, wall means defining a chamber provided with an inlet and an outlet and having a lower zone and an upper heat treating zone; elongated tubular guide means eX- tending between said inlet and said outlet in said lower zone and having an upper wall portion facing said upper zone and provided with a longitudinally extending slot, and a lower wall portion opposite said upper wall portion and provided with a longitudinally extending groove arranged for accumulation therein of solid contaminants descending through said slot; carrier means located and guided for movement within said tubular guide means in an upright position from said inlet to said outlet and comprising a workpiece supporting portion extending through said slot into said heat treating zone for supporting a workpiece to be heat treated therein, and a pusher portion extending into said groove for pushing accumulated contaminants along the same and to said outlet; and return guide means constructed and arranged for guiding said carrier means for return movement from said outlet to said inlet.

References Cited UNITED STATES PATENTS 1,362,369l 12/1920 Talley 263--6 1,799,571 4/1931 Smith 263-8 3,331,593 7/1967 Rea 263--8 3,434,702 3/1969 Krause 263-8 JOHN I. CAMBY, Primary Examiner 

